SSL Issues with a Blazor App Running On IIS

Biggers 0

I have a Blazor Server applictaion running on IIS using an Origin SSL certificate. We also manage our domains through Cloudflare. Everything was working perfectly for roughly two weeks on a new server, and over a month on an older server. Then we started experiencing some serious issues:

Recently we have had ocassional issues with Cloudflare kicking back a 526 error, an error specific to Cloudflare noting that they are unable to validate the SSL certificate. The cert is valid, as other sites are using it as well. The problem is intermittent, and once it occurs on the Blazor site, the other sites on the domain also hosted in IIS start to have issues as well (most notably, not loadig javascript files) and/or the 526 Error (invalid SSL Certificate).

It is a NetCoreApp3.1 project. Blazor Server.

MotoX80 31,571 Reputation points

2023-02-07T20:11:16.3933333+00:00

Is the time of day clock on your server correct?
XuDong Peng-MSFT 10,096 Reputation points Microsoft Vendor

2023-02-08T02:53:30.9966667+00:00

Hi @Biggers,

You mentioned that the problem is intermittent, I'm afraid I can't determine the cause of the problem, have you tried generating a report with SSL Diagnostics to try and narrow down the problem?

In addition, have you tried changing the SSL/TLS encryption mode from Full (Strict) to Full in Cloudflare? I found such a solution in a similar problem. Does this problem only happen on this Blazor site, or does it happen to other sites as well?
Lex Li (Microsoft) 4,662 Reputation points Microsoft Employee

2023-02-16T06:02:09.01+00:00

Your best guide here is Cloudflare support, who has access to all the needed logs to identify the cause. There isn't much you or Microsoft can do here, as the error response origins from Cloudflare, but you do need to upgrade to .NET 6/7, as .NET Core 3.1 reached end of life.